1. Field of the Invention
The present invention relates to a technology for supporting an upstream communication and simultaneously enabling easy analysis of an optical signal using identification information about an optical network terminal (ONT) by transmitting an upstream optical signal including the identification information.
2. Description of the Related Art
A recent large-scale multimedia service or Internal Protocol television (IPTV) service may provide data to a subscriber end through an optical line in an optical subscriber network. Among optical subscriber networks, a passive optical network (PON) including a passive device that uses little power supply halfway is widely used due to easy maintenance and economic feasibility.
Monitoring a state of a network is necessary for reliable management of a PON. For example, since a cut of an optical fiber cable in the network, deterioration, a structure change of a connector, and the like may cause communication problems between an optical line terminal (OLT) and an optical network terminal (ONT) connected through the network, monitoring changes in the network is required.
A conventional optical time domain reflector (OTDR), an apparatus for monitoring a state of a network, may analyze a state of an optical line in the network, for example, an error location and characteristics. That is, the OTDR may analyze the state of the optical line, by transmitting an optical signal, for example, an optical pulse, having a predetermined wavelength to the optical line, and measuring an optical power of the pulse that is backscattered due to Rayleigh scattering, Fresnel reflection, and the like. The conventional OTDR may be disposed, for example, in an ONT to analyze the state of the optical line in the network. Here, since the OTDR may require an optical signal having an optical wavelength distinct from optical wavelengths of an upstream optical signal and a downstream optical signal, for example, an optical signal in a 1,600 nanometer (nm) band, a cost of the equipment may increase.
Accordingly, there was suggested a low-cost OTDR that may reduce such a cost of equipment, through common use of an upstream optical signal of an ONT as an optical signal for monitoring. That is, when an upstream optical signal is not transmitted by an ONT connected to an OLT, the low-cost OTDR may transmit, to an optical line, an optical signal for transmitting data as an optical signal for monitoring, and may analyze discontinuity of the optical line using reflected pulse lights, thereby verifying a state of the optical line.
However, such a low-cost OTDR may fail to verify the state of the optical line when an upstream communication is performed such that an upstream optical signal is transmitted. Accordingly, when an unexpected error, for example, a fiber-cut or fiber-bending, occurs, the low-cost OTDR may fail to detect the error in real time.
In addition, when an upstream optical signal transmitted from another ONT is reflected due to discontinuity, that is, an error, occurring in the optical line, reflected pulse lights may be mixed to be indistinguishable from one another. In this case, the low-cost OTDR may face a difficulty in analyzing the state of the optical line accurately.